Effect of gas flow on the temperature rise of a micro-beam-type thermal conductivity detector

We have proposed a "micro-beam" MEMS sensor for measuring the thermal conductivity of gases and liquids. It is a beam-shaped metallic foil sensor, approximately 10 μm in length, that is built over a trench on a silicon substrate. The principle of the measurement is to determine the thermal conductivity of a sample from the temperature rise of the sensor at a steady state, which is achieved within a millisecond. Potential application of the sensor would be gas sensors and gas chromatography, where the sensor is exposed to a gas flow. Hence the objective of the present study is to examine the effect of flow on the temperature of the sensor. A chip with a platinum sensor fabricated on its surface was embedded in a flat PVC plate and placed in the potential core of an air flow from a nozzle. The electrical resistance of the sensor was measured by a four-wire technique with heating the sensor with DC current. The results showed that the temperature rise at a given heating rate, which indicates the heat dissipating potential to the air, did not change with increasing the air velocity. It also agreed well each other irrespective of the angle of attack or the length from the leading edge. The results demonstrated that the temperature rise of the sensor was independent of the air flow, suggesting that the heat dissipation was governed only by the heat conduction to the air.